The strangest thing I learned today is that polar bears have see-through fur. This does not mean that they will be green if they are standing on a green lawn, however. They will still appear white due to the way their transparent fur scatters light, but they can sometimes appear green if they have a green algae getting in the fur, which they sometimes do get when things get hot.
Ask any child what color a polar bear is and s/he will exclaim, “white” with great enthusiasm, but truth be told, their fur is actually transparent and holds no color. It only appears white because it reflects visible light.
They’re nearly invisible under infrared photography. Polar bear skin, surprisingly however, is black! To humans and other creatures that see only in visible light, polar bears nearly blend in seamlessly with their snowy environment. However, reindeer have outsmarted the polar bear’s tricky fur by evolving a visual system than can see in ultraviolent light, which means polar bears stand out like a sore thumb against their icy white backdrop.
In zoos you may have noticed that polar bears have almost yellow or green-tinged fur. The yellowing of the fur is due to age and dirt, while the greenish color is from the algae that can grow on polar bear fur in unnaturally warm and humid environments.
But if the Polar bear’s skin is black, how come they don’t look black in colour? Well, each of the longer guard hairs on the Polar bear’s body is hollow and reflects visible light, much like snow. So when the sun is shining brightly, Polar bears appear bright white.
This polar bear has algae growing in its hair. Photo Credit: Steven Pierson
Since these hairs are hollow, the Polar bears’ diet and environment can affect their colour. Polar bears whose diet has a lot of seals in it can look light yellow because of the seal oils. Polar bears that live in warmer climates (like in zoos) can have algae growing in their hair, which can make them look green! Don’t worry, being green doesn’t cause the Polar bear any harm and a bath with special salt solution turns them white again. …
Polar bears are white, but their hair is mostly clear! To recap … when light shines on the Polar bear’s mostly clear guard hair, some light gets trapped in the hair and bounces around, creating luminescence. When it hits a light scattering particle on the inside or salt on the outside, the light breaks up even more and gets sent in all different directions. This light scattering gives off more white-coloured light due to luminescence. UV light also gets transmitted along the guard hairs onto the bear’s dark skin, causing florescence and don’t forget about the keratin protein whose molecules give off a slight white colour. Each of these elements brings you the white Polar bear you know and love.